1. Field of the Invention
The present invention relates generally to ladders, ladder systems and ladder components and, more specifically, to combination ladder rail configurations, ladder support structures, ladder hinge configurations and methods of manufacturing the same.
2. State of the Art
Ladders are conventionally used to provide a user thereof with improved access to locations that might otherwise be inaccessible. Ladders come in many shapes and sizes, such as straight ladders, straight extension ladders, step ladders, and combination step and extension ladders. So-called combination ladders are particularly useful because they incorporate, in a single ladder, many of the benefits of other ladder designs.
However, the increased number of features provided by a combination ladder also brings added complexity and manufacturing difficulties in producing such a ladder. Additionally, the incorporation of additional features in a ladder often leads to an increase in the weight of a given ladder or ladder system. Generally, since ladders are used as portable tools, added weight is often an undesirable attribute in ladders. Further, since a combination ladder may be used in various configurations and, thus, experience various loading conditions, the ladder's components may require higher strength materials or may need to be increased in size over a conventional non-combination ladder to accommodate such loading requirements. Thus, combination ladders or ladder systems may ultimately cost more and/or weigh more than conventional ladders or ladder systems.
For example, in order to support a combination ladder, the lower portions of the outer side rails are conventionally flared by bending a lower portion of the outer side rails outwardly so as to increase the lateral distance therebetween. While such a configuration serves to increase the stability of the ladder, successfully forming the flared outer side rails presents various manufacturing complexities. For example, if the outer rails are formed with a conventional fiberglass composite material, the bending of such members may result in weakening or potential breakage of individual fiberglass strands and, ultimately, lead to the premature failure of the outer rail in which the bend is formed.
In order to form a bent side rail which is fabricated from conventional fiberglass composite materials and which meets quality and structural design requirements, the side rail may need to be molded including the individual placement of fibers within the mold. Such a process is both labor and time intensive. For example, in order to provide sufficient strength in such outer side rails, U.S. Pat. No. 4,371,055 to Ashton et al. discloses a manufacturing method in which fibers are angularly oriented relative to a longitudinal axis of the resulting side rail. However, as noted above, such a method requires a time and labor intensive molding process and, additionally, requires the use of custom molds. Even in the case of forming a bend in metal side rails, additional equipment is required to properly form such a bend without impairing the structural integrity of the components.
Another concern in the manufacture of a combination ladder, or any ladder, is providing the ladder with sufficient rigidity. In other words, the side rails and other ladder components should not exhibit excessive deflection, either in bending or in torsion, while under loaded conditions. One prior art approach for improving the rigidity of a ladder includes providing a support brace that extends, for example, between the lower side rails and attaches to a rear face of each. Thus, when a ladder experiences loading, a portion of the loading may be transmitted to such brace, helping to maintain the two side rails from becoming displaced outwardly from one another. Another prior art approach has been to provide a pair of braces, each of which extends between a lower rung of the ladder and a front wall or a rear wall of an outer rail of the ladder.
However, prior art support braces such as those described above conventionally include relatively long, thin strips of material. Such bracing is often susceptible to bending, twisting and buckling due to potential exposure and abuse of the bracing associated with the general handling, storing and transportation of the ladder. Additionally, such bracing may be obstructive, and thus pose a safety hazard, to the user of the ladder in certain instances.
Yet another difficulty in designing and manufacturing a combination ladder involves the hinges of such a ladder. Prior art approaches for simplifying ladder hinges have included the use of multiple plates to form the primary structural elements of the hinge. The multiple plates may be positioned within the hollow portion of a side rail and then fixed therein such as by rivets or similar fasteners. However, as the user of the ladder applies a force to the side rail, such as in changing the configuration of the ladder from a step ladder to an extension ladder, the force is transmitted to the hinge member in large part through the fasteners (e.g., the rivets). The fasteners thus become a critical structural element of the ladder and are susceptible to fatigue and wear due to the cyclical loads applied thereto.
Considering the desire to maintain or decrease the cost, weight, and complexity of combination ladder systems while maintaining, or even improving, the structural soundness of such ladder systems, it would be advantageous to provide a ladder system having, for example, improved hinge mechanisms, support structures, and extension rail configurations.